Squeak Etoys is a "media authoring tool"-- software that you can download to your computer
and then use to create your own media. You can write out your project and share it with others.
Etoys runs on any Mac or Windows machine, as well as on the OLPC XO machine.
It is free.
Find out about Etoys.

Text of this guide (for searching): Script Tile: X and Y Tiles Mark Places on a Grid
This red oval is assigned to an exact location on the X axis in the Guide.
Try the oval on the world and find X=212 there.
Move it left or right and it returns. Click and hold down on the X in the tile below.
A menu opens, choose increase by.
Click on the green clock to start and stop the script. Choose X decrease by from the same tile menu and start the script. Experiment. How far will it go?
Click on the number in the blue and green tile; type in a new value. Press Enter on the keyboard. The green oval is there.
Or, start the script and watch. infinity?.